Chemical reactions are routinely carried out by contacting one or more reactants with a catalyst at an elevated temperature and/or pressure. Ordinary reaction vessels heat or cool reactants before charging the reactants to a reaction zone to provide a suitable temperature for the reaction to occur. The reactions that occur are typically endothermic or exothermic in nature so that in order to achieve a suitable average temperature the reactants usually enter the reaction zone at a temperature above or below an optimal temperature for the reaction and/or leave the reaction zone at a temperature below or above an optimal temperature. The time that the reactants contact the catalyst at excessive or deficient temperatures negatively impacts the reaction. Negative impacts include catalyst activity losses and poor product selectivity.
Many prior art processes ameliorate the adverse temperature effects by dividing a reaction section into several separate zones to adjust the temperature of the reactants between zones by interstage heating or cooling. Interstage heating or cooling of the reactants between multiple reaction zones reduces the magnitude of the temperature variations but still does not completely solve the problems of excessive or deficient temperatures. In addition, some endothermic reactions would benefit from a rising temperature profile while passing through a catalyst bed. Interstage heating cannot provide a rising temperature profile for such endothermic reactions. Thus, chemical reactions can be carried out more effectively by maintaining a constant or increasing temperature profile for the entire time the reactants contact the catalyst.
The use of heat exchange elements within a catalyst bed are known to provide a more constant temperature for reactants in the catalyst bed. These heat exchanger reactors can maintain favorable reaction temperatures throughout a reaction zone. U.S. Pat. No. 4,810,472 depicts a bayonet tube arrangement for externally heating a reformer feed that passes through catalyst on the inside of the bayonet tube. U.S. Pat. No. 4,256,783 illustrates an arrangement for catalytic oxidation using multiple catalyst filled tubes immersed in a cooling fluid to control reaction temperatures. U.S. Pat. No. 4,743,432 discloses a reactor for the production of methanol having catalyst disposed in beds for contact with the reactants and cooling tubes passing through the beds for the removal of heat.
Although tubes are widely proposed to retain catalyst and reactants, or a heat exchange medium in heat exchange reactors, plate type heat exchange elements can provide greater and more effective heat exchange surface. U.S. Pat. No. 3,127,247 shows the use of cylindrical plates to form alternate annuli of heat exchange medium and catalyst in a heat exchanger reactor. U.S. Pat. No. 4,820,495 depicts a synthesis reactor for ammonia or ether production having adjacent elongate compartments alternately containing a heat carrier fluid and catalyst and reactants.
Similar to the arrangement disclosed in U.S. Pat. No. 4,820,495, a layered construction of substantially parallel plate heat exchange elements provides an effective arrangement of channels. In such arrangements every other channel contains catalyst through which reactants pass while a heat transfer fluid passes through the channels that do not contain catalyst. These channels offer a highly efficient heat transfer arrangement for controlling catalyst and reactant temperatures in catalytic processes. Since most of the catalytic reaction processes operate at elevated pressures, cost effective containment of the reaction process relies on cylindrical pressure vessels to house the catalyst and heat exchange elements. The most productive forming processes for the plate heat exchange elements yield thin, corrugated heat exchange elements in the form of substantially flat plates. Using indirect heat exchange to maintain a temperature that remains constant or opposes the heat effects of the reaction requires narrow reactant channels.
Arranging a large number of thin heat exchange plates to create narrow heat exchange channels poses mechanical and processing problems. The reactant channels must provide enough surface area to compensate for the loss of temperature differential between the reactants and the heat exchange fluid at the heat exchange fluid outlet. In addition the reactants and the heat exchange fluid may have different pressures that impose a differential loading across the plates. The plate elements must withstand differential pressure without excessive distortion. However from a structural standpoint flat plate elements operate inefficiently to withstand the normal loading from pressure differentials. Without adequate support the differential pressure loading can deform the thin plates. Moreover indirectly heating or cooling reactants adds additional distribution and collection conduits that further compound the problems of providing incorporating thin plate heat exchange elements into a reactor.
It is an object of this invention to provide an arrangement of heat exchanger reactor internals having radial fluid flow through narrow channels that is simple to construct and overcomes the problems of plate support and conduit arrangement for the supply and withdrawal of both heat exchange medium and reactants.